For a standard 15A residential circuit, use 14 AWG copper wire. For 20A, use 12 AWG. For 30A, use 10 AWG. If you are sizing for a 50A EV charger or range, use 6 AWG (assuming 75°C terminals). This electrical cable size and amp chart gives you the exact numbers from the National Electrical Code (NEC) to size your branch circuits and feeders without guessing.
How to Read This Electrical Cable Size and Amp Chart
The chart below is derived directly from NEC Table 310.16. It lists the allowable ampacities for insulated copper conductors rated up to 2000 volts. To use it correctly, you must understand the three temperature columns:
- 60°C (140°F): Applies to older insulation types (TW, UF) and, crucially, to all 14, 12, and 10 AWG wires regardless of their actual insulation rating, per NEC 240.4(D).
- 75°C (167°F): Applies to common commercial/residential terminations and wire types like THHW and THWN. Most modern breakers and receptacles are rated for 75°C.
- 90°C (194°F): Applies to premium insulation like THHN and XHHW. You cannot use this column to size your overcurrent breaker for small wires. The 90°C column is only used as the starting baseline for derating calculations.
I have seen apprentices pull 10 AWG THHN for a 35A HVAC condenser because the 90°C column says 40A. But NEC 110.14(C) dictates that termination limits govern the final ampacity. If the breaker terminal is rated 75°C, you are capped at 35A. If it is an older 60°C panel, you are capped at 30A, and that 35A load will eventually trip the breaker or melt the lug.
The Master Chart: NEC Table 310.16 Copper Ampacities
The following table assumes an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway or cable.
| AWG / kcmil Size | 60°C Column (TW, UF) | 75°C Column (THHW, THWN) | 90°C Column (THHN, XHHW) |
|---|---|---|---|
| 14 | 20A * | 25A * | 30A * |
| 12 | 25A * | 30A * | 35A * |
| 10 | 30A * | 35A * | 40A * |
| 8 | 40A | 50A | 55A |
| 6 | 55A | 65A | 75A |
| 4 | 70A | 85A | 95A |
| 3 | 85A | 100A | 115A |
| 2 | 95A | 115A | 130A |
| 1 | 110A | 130A | 145A |
| 1/0 | 125A | 150A | 170A |
| 2/0 | 145A | 175A | 195A |
| 3/0 | 165A | 200A | 225A |
| 4/0 | 195A | 230A | 260A |
* Note: Per NEC 240.4(D), the maximum overcurrent protection for 14 AWG is 15A, for 12 AWG is 20A, and for 10 AWG is 30A, regardless of the higher ampacities shown in the 75°C and 90°C columns.
Bookmark-Friendly Quick-Jump Rows
- 15A Lighting/Receptacle Circuit: 14 AWG (60°C column baseline).
- 20A Kitchen/Bathroom Circuit: 12 AWG (60°C column baseline).
- 30A Dryer/Water Heater: 10 AWG (60°C column baseline).
- 40A Range/Cooktop: 8 AWG (Use 75°C column if terminals are rated for it; otherwise 6 AWG for 60°C).
- 50A EV Charger/Hot Tub: 6 AWG (75°C column yields 65A, allowing a 50A breaker).
- 100A Subpanel Feeder: 3 AWG (75°C column yields exactly 100A).
Derating Rules: When Base Ampacity Drops
The numbers in the master chart are best-case scenarios. On a real jobsite, two factors force you to derate (reduce) the wire's capacity: ambient temperature and conductor bundling. According to the Copper Development Association, pushing current through copper generates heat; if that heat cannot dissipate, the insulation degrades and fails.
1. Conductor Bundling (NEC Table 310.15(C)(1))
When you pull more than three current-carrying conductors through a single conduit, the mutual heating effect requires you to multiply the base 90°C ampacity by a derating factor.
- 4 to 6 conductors: Multiply by 80%
- 7 to 9 conductors: Multiply by 70%
- 10 to 20 conductors: Multiply by 50%
Worked Example: You are pulling four 8 AWG THHN wires (two hots, one neutral, one ground) through a conduit for a multi-wire branch circuit. The ground does not count as a current-carrying conductor, leaving three. No derating is required. However, if you add a second circuit (four hots, one neutral = 5 current-carrying conductors), you must apply the 80% factor to the 90°C column.
Math: 8 AWG THHN 90°C base = 55A. 55A × 0.80 = 44A. You can safely protect this wire with a standard 40A breaker.
2. Ambient Temperature (NEC Table 310.15(B)(1))
If your conduit runs through a hot attic where temperatures reach 50°C (122°F), you must multiply the 90°C ampacity by 0.82. Always apply both temperature and bundling derating factors if both conditions exist, then select a breaker that does not exceed the final calculated ampacity.
Decision Path: Pick Your Exact Wire Gauge
Use this decision tree to lock in your wire size and breaker combination. This path assumes copper wire, standard residential terminations, and an ambient temperature under 30°C (86°F).
| Step 1: Determine Load Type | Step 2: Calculate Minimum Ampacity | Step 3: Select Wire (Copper) | Step 4: Select Breaker |
|---|---|---|---|
| Non-Continuous (Under 3 hours, e.g., disposal, standard outlets) | Load Amps × 1.0 | Match or exceed load in 60°C column (for 14-10 AWG) or 75°C column (for 8 AWG+) | Next standard breaker size ≥ Load |
| Continuous (3+ hours, e.g., EV charger, baseboard heat, commercial lighting) | Load Amps × 1.25 | Match or exceed the calculated ampacity in the 75°C column | Next standard breaker size ≥ Calculated Ampacity |
Concrete Pick Example: You are wiring a 40A continuous-load EV charger.
1. Calculate: 40A × 1.25 = 50A minimum ampacity required.
2. Select Wire: Looking at the 75°C column, 8 AWG is rated for 50A. (If your EV charger terminals are only rated 60°C, you must step up to 6 AWG, which is 55A).
3. Select Breaker: 50A standard breaker.
Final Bill of Materials: 8 AWG THHN (or 6 AWG NM-B) and a 50A double-pole breaker.
What This Chart Cannot Tell You
An ampacity chart guarantees the wire will not melt under normal conditions, but it does not guarantee performance. Keep these three blind spots in mind before pulling wire:
- Voltage Drop: NEC 310.15(B) provides ampacity, but NEC 210.19(A) Informational Note recommends keeping voltage drop under 3% for branch circuits and 5% total. If you are running a 120V, 15A circuit to a shed 150 feet away, 14 AWG will safely carry the current without catching fire, but the voltage at the shed will drop below 114V, causing motors to overheat and lights to dim. For runs over 100 feet, always run a voltage drop calculation and typically bump up one or two AWG sizes.
- Aluminum vs. Copper: This chart is strictly for copper. If you are buying SER cable or MHF for a 200A service entrance or a large subpanel feeder, you will likely use aluminum to save money. Aluminum has higher resistance; you must use NEC Table 310.16's aluminum columns, which generally require a wire two AWG sizes larger than the copper equivalent (e.g., 4/0 Aluminum for a 200A residential service, compared to 2/0 Copper).
- Short Circuit Let-Through Current: Ampacity charts deal with thermal heating over time. They do not tell you if the wire can survive the magnetic and thermal stress of a 10,000A short circuit before the breaker trips. That is governed by the breaker's interrupting rating and the wire's short-circuit withstand curve.
The Final Default: If you are ever in doubt, cannot read the terminal temperature stamp on your breaker or receptacle, or are working in an older home with unknown hardware, default strictly to the 60°C column. It is the most conservative path, universally accepted by inspectors, and guarantees you will never undersize the conductor for the termination hardware.
